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Check out this article in the print edition of StudentFilmmakers Magazine, November 2007. Click here to get a copy and to subscribe >>

Visual Effects through Color Enhancing Filters
Seeing Red

by Ira Tiffen

The painter needs more intense color; he gets a tube of it at the store. The cameraman with the same need gets a filter: a color enhancing filter. Color enhancing filters are for the times when the palette offered to us by our camera does not match our vision.

Increasing color intensity is the result of paring away extraneous wavelengths of color, emphasizing the colors closely surrounding the central color we desire. This is true of paint, as well as of optical filters.

The most often-used color enhancer is made from a combination of two rare-earth mineral elements, neodymium and praseodymium. The combination is usually referred to as didymium. These are incorporated into the molten glass, which is cooled and machined into an optical filter element. In the right proportions, didymium filters can enhance reddish colors, turning brick, barn and rust reds into more intense crimson and scarlet. Some oranges are also affected; bright red objects hardly at all.

In the color spectrum, most of what we see can be said to be made up of various combinations of red, green and blue. Red centers around 650 nanometers (nm); green around 550 nm; and blue around 450 nm. Reddish objects, as opposed to red objects, reflect portions of the spectrum between red and green, which turn them into various brownish reds. You know that when you mix red and green paint, you get brown. The red enhancer pulls out most of the light between 570 nm and 620 nm. This increases the proportion of more intense red light reflecting back to the camera.

Most famous for making the most of fall foliage, the red enhancer manages to maintain a generally neutral color elsewhere, while it intensifies reds. Skin tones may become warmer; whites may take on a slight magenta cast. The effect does differ depending on the color temperature of the ambient light and the color sensitivity of the recording medium. Mild color correction afterward will balance out any discrepancies while retaining the effect on reds. In addition, these filters require exposure compensation of about one stop; for more details check with the manufacturer.

Other rare earth elements have the ability to affect light in a similar manner to intensify other colors, such as blue and green. One of these is also shown along with a red enhancer in the accompanying images.